There has long been a desire to formulate a curing agent which is essentially free of volatile organic compounds (VOC's), which are self emulsifiable and curable at a wide range of temperatures in the absence of external accelerators if possible.
Many of the current water borne epoxy resins and curing agents are plagued with the problem of poor film properties because the surfactants tend to migrate to the surface during the cure of the resin system. Thus, it would be desirable to provide a curing agent system containing a surfactant which does not migrate during cure, that is, a self emulsifiable system which does not require salting the surfactant or using plasticizers to stably disperse the curing agent in water.
In addition to providing a self emulsifiable water borne curing agent, the curing agent should be readily compatible with a water borne epoxy resin in order to make a coating having good mechanical properties and weatherability. A water borne curing agent that does not have good compatibility with the epoxy resin will not coalesce well when applied onto a substrate. The problem of compatibility is more acute where the curing agent primary amine groups have been converted to secondary amine groups to reduce the blooming or hazing phenomena.
Further, in view of the continuous need to provide curing agents which are environmentally friendly, the self emulsifiable curing agent should contain little or no VOC's, that is, be dispersed in water or other non-VOC, without the need to use co-solvents to solubilize the curing agent. Moreover, the surfactant used to disperse the curing agent should be effective to disperse large quantities of the curing agent to provide a high solids level. Of course, the water borne curing agent should also be stable, at least long enough to mix, store, ship and apply.
It is also desirable that the water borne curing agent cure water borne epoxy resins at ambient temperatures, preferably without the use of external accelerators or catalysts. This would reduce the overall cost of the system and avoid the potential for migration of catalyst from the coating. Thus, the curing agent should be sufficiently reactive so that accelerators are not needed for room temperature cure, but not excessively reactive that on loses the pot life needed for applying or working with the system.